Almost every type of rechargeable battery (lead-acid, nickel-cadmium, nickel-metal hydride, lithium, etc.) can be damaged and/or its operating capacity can be reduced by what is often referred to as overcharging. Many such devices, the chargers for such batteries, and sometimes even the batteries themselves, are provided with indicator lights or other alerts to inform the user that the battery is fully charged, prompting a user that the device or battery should be removed from the charger once charging is complete. Further, the instruction manuals of almost every such device include warnings, some of them prominent, that the device not be overcharged and/or that the device should be removed from the charger or power source when the charge indicator appears.
In actual practice, however, the users of devices that are powered by rechargeable batteries tend to leave the battery, or the device including the battery, on the charger or connected to a power source from the time charging starts until the device or battery is unplugged for subsequent use. As a result, the battery is often left on the charger and/or the device including the battery stays connected to a power source for many hours longer than needed to recharge the battery (newly-developed battery technology has produced batteries that charge in minutes rather than hours with the result that the battery and/or device stays on the charger far longer than necessary), despite the prominent warnings against overcharging.